Description of the Prior Art
In presently known disk drives, magnetic head assemblies are employed for coacting with a rotating magnetic disk to record and read data signals. Magnetic head assemblies that fly over the rotating disk at a predetermined head-to-disk spacing generally incorporate slider elements formed with longitudinal rails. The air bearing configuration of the sliders allows an aerodynamic force to be applied to the magnetic head so as to urge the head away from the surface of the rotating disk. A load force provided by a flexure or spring opposes the aerodynamic force and the resultant of the two opposing forces determines the flying height of the magnetic head.
A major objective in disk drive technology is to increase the packing density of the data recorded on the disks. One factor that enables an increase in data density is the length of the transducing gap which is made as small as possible so that short wavelength, high frequency data signals can be recorded. To realize higher frequency recording, thin film transducers are preferably used. Of prime importance in the production of thin film heads is the distance from the apex of the insulation between the pole pieces of the head structure to the end of the transducer located at the lapped surface of the head slider rails. This distance is defined in the industry as the throat height, measured from zero throat height at the apex. It is highly desirable to obtain a predetermined throat height which affords optimum magnetic characteristics for the magnetic head and can be uniformly and repetitively produced. During manufacture of the magnetic head sliders, thin film transducers are deposited in rows on a ceramic substrate. The substrate is then sliced into longitudinal sections or rows, each row having a multiplicity of aligned thin film transducers. Each substrate section or row is separately bonded to a transfer tool, by epoxy for example, and configured into individual sliders with longitudinal rails. A thin film transducer is disposed at the trailing edge of each rail. During slicing of the rows, substantial distance in the order of 0.001 to 0.0022 inches must be maintained between the cutting edge of the saw element and the desired throat of the magnetic transducer to avoid damage to the transducer. The excess material is then removed by fine grinding or preferably by a lapping process. The final predetermined throat height ranges from 40 to 100 microinches depending upon the transducer design. The final predetermined throat height typically has a tolerance of .+-.20 microinches, with a specified tolerance of .+-.10 microinches being preferred.
Each row of sliders is lapped by use of a lapping machine with a planetary motion, while they are positioned in alignment on a transfer tool, to establish a predetermined throat height for each transducer. As the lapping machine laps or grinds the slider elements and the pole tip area of the thin film transducers, the throat height of each transducer is progressively reduced. The throat height level is monitored, either by visual means such as a microscope; or by high resistance elements and electrical lapping guides (ELGs) to produce electrical signals for controlling the lapping operation. When the desired throat height is reached, the lapping procedure is halted and the lapped and configured sliders with thin film transducers, each having a predetermined uniform throat height, are removed from the transfer tool by use of a solvent, by way of example.
FIGS. 1 and 2 depict a transfer tool 10 which is widely used in the industry for thin film head fabrication. The tool 10 is made from a rigid metal block, which may be a two inch long stainless steel piece formed with a crenelated configuration of evenly spaced rectangular blocks 11 on a top surface. Apertures 14 are provided for mounting the tool 10 to a plate (not shown) to enable lapping and machining of a slider bar 12 made of a ceramic material. Thin film transducer assemblies 20 and electrical contacts 26 are uniformly spaced on the slider bar 12, as illustrated in the enlarged FIGS. 3A and 3B. During fabrication, the bar 12 which is bonded in place on the top surface of the transfer tool 10, is lapped, sectioned and configured to produce a row of sliders 18.
During the lapping process, there is minimal flexing of the tool body, but as a result of the stress induced in the material of the tool, curvature or bow of the row of sliders occurs. The curvature can be concave or convex, which may be defined respectively as a negative bow or positive bow. To ensure that the sliders are being lapped uniformly so that the throat heights of the thin film transducers are substantially the same, it is necessary to present a collinear array of transducers along the slider bar 12 to the lapping plate.
In addition, the adhesives used during row bonding across the length of the slider bar tend to contract during the lapping process. Therefore it becomes virtually impossible to realize the relatively tight tolerances of .+-.10 to 20 microinches. The transfer tool presently used in the industry typically obtains throat height tolerances of up to .+-.60 microinches which does not produce sliders with thin film transducers having optimum throat height and good operating magnetic characteristics.